Composite pane and method for producing the composite pane

ABSTRACT

A composite pane includes a first pane, a second pane, and a thermoplastic film arranged between the two panes, wherein at least one pane is in the form of a flat glass and at least one pane surface has a plurality of elongated elevations and elongated depressions that extend along a first pane direction and are alternatingly arranged in a second pane direction perpendicular to the first pane direction, the thermoplastic film is produced by extrusion and at least one film surface has a plurality of elongated elevations and elongated depressions that extend along a first film direction and are alternatingly arranged in a second film direction perpendicular to the first film direction, wherein the elongated elevations of the at least one pane are arranged at an angle different from 90° relative to the elongated elevations of the thermoplastic film.

The invention relates to a composite pane and a method for producing thecomposite pane.

Composite panes, in particular those for use as a windshield of a motorvehicle, have two panes and at least one thermoplastic film situatedbetween the two panes. Usually, at least one pane is in the form of flatglass, which is frequently produced in industrial series production inthe float glass method.

In the float glass method, molten glass is routed from one side onto abath of liquid tin (float bath). For example, the temperature at theinlet of the tin bath is approx. 1000° C. The lighter molten glassfloats on the tin and spreads evenly on the tin surface. As result ofthe surface tension of the tin, the glass forms a very smooth surface.At a cooler end of the tin bath, the solidified glass is continuouslypulled out in strip form and then cooled. After sufficient cooling,glass sheets are cut to length from the glass strip in the desired size.

The distribution of the molten glass on the tin bath determines anequilibrium thickness of the glass, which is, however, too large formany applications. In order to reduce the pane thickness, the alreadysolidified glass is pulled out of the tin bath by actively driven (top)rollers, achieving elongation of the glass strip. Here, the thickness ofthe glass can be adjusted by the speed of the rollers, wherein a higherspeed is set for producing thinner glasses and, correspondingly, a lowerspeed of the rollers is set for thicker glasses.

As is known to the person skilled in the art, the glass produced in thefloat glass method has a certain unevenness or waviness of its surfacesas a result of being pulled out of the tin bath. Accordingly, both glasssurfaces have elongated elevations and depressions in a parallelarrangement, which extend in each case in the direction of the pullingof the glass strip from the tin bath. The elongated elevations anddepressions correspond to wave crests and wave troughs that are arrangedalternatingly and perpendicular to the pulling direction. Theseelongated structures of the glass are also known to the person skilledin the art as “float lines”. The thinner the glass, the greater thepulling action on the glass strip has to be, resulting, in turn, in thefact that the float lines are more pronounced. In industrial seriesproduction of flat glass, rectangular glass sheets are typically cut tolength with their longer dimension in the direction of the strip suchthat the float lines extend parallel to the longer dimension of theglass sheets.

Also known is the industrial production of thin glasses by the fusiondraw method. Therein, the molten glass is typically withdrawn downwardfrom the melting furnace via an outlet nozzle by rollers. In the fusiondraw method, analogously to the float glass method, elongated elevationsand depressions of the glass surfaces develop, corresponding to wavecrests and troughs that are arranged alternatingly and perpendicular tothe pulling direction such that, here as well, the glass surfaces have aslight waviness. These elongated structures of the thin glasses producedin the fusion draw method are known to the person skilled in the art as“draw lines”.

The thermoplastic films that are produced by extrusion are alsotypically characterized by undesirable production-related waviness. Thismanifests itself in the form of thickness changes (elongated elevationsand depressions) transverse to the direction of extrusion. Thisundesirable waviness must be distinguished from intentionally producedroughness, which is typically embossed into the thermoplastic film topromote deaeration of the layer stack during production of the compositepane. The unwanted waviness and the intentionally produced roughnessdiffer substantially in terms of the distance between adjacent elongatedelevations or elongated depressions. The intentionally producedroughness is described, for example, in EP 3 029 000 A1, EP 3 029 001A1, EP 3 029 002 A1, EP 3 029 003 A1, EP 2 881 376 A1, EP 2 674 295 A1,WO 2016/030284 A1, WO 95/19885 A1, and WO 2008/003789 A1.

In practical application, the float lines or draw lines can result in anadverse effect on the optical properties of the flat glass since thewaviness of the flat glass causes a lens effect with locally differentoptical refractive power. This is particularly pronounced when the floatlines or draw lines unfavorably overlap with the production-relatedwaviness of the thermoplastic film. For example, in the case ofwindshields in motor vehicles, when the head is inclined from one sideto the other or from up to down, objects viewed through the windshieldcan appear distorted due to the locally different optical refractivepower.

The object of the invention is to provide a composite pane with improvedoptical properties as well as a method for producing such a compositepane.

These and other objects are accomplished according to the proposal ofthe invention by a composite pane with the features of claim 1.Advantageous embodiments of the invention result from the dependentclaims.

The present invention presents a composite pane, in particular acomposite pane that comprises a first pane, a second pane, and at leastone thermoplastic film arranged between the two panes. At least one ofthe two panes is in the form of a flat glass and has on at least onepane surface, in particular on both pane surfaces, a plurality ofelongated elevations (wave crests) and elongated depressions (wavetroughs) related to its production, which extend along a first (pane)direction and are arranged alternatingly in a second (pane) directionperpendicular to the first (pane) direction. The first direction usuallycorresponds to a pulling direction in the production of a glass stripfrom which the pane is formed, for example, the direction of pulling outof the float bath (tin bath) of a pane produced in the float method (theelevations or depressions correspond to the float lines) or thedirection of pulling out of the melt strip of a thin glass produced inthe fusion draw method (the elevations or depressions correspond to thedraw lines). The elongated elevations and elongated depressions of thepane are typically parallel to one another and arranged in alternatingsequence.

The thermoplastic film of the composite pane according to the inventionis produced by an extrusion method, in which plasticized material isdelivered in the form of a film from a extruder apparatus. Thethermoplastic film also has a certain waviness or unevenness of thesurface related to its production. Thus, at least one film surface, inparticular both film surfaces, of the thermoplastic film has a pluralityof elongated elevations (wave crests) and elongated depressions (wavetroughs) that extend along a first (film) direction and arealternatingly arranged in a second (film) direction perpendicular to thefirst (film) direction. The first direction corresponds to the extrusiondirection of the thermoplastic film. The elongated elevations andelongated depressions of the thermoplastic film are typically parallelto one another and arranged in alternating sequence.

In the context of the invention, the elongated elevations (wave crests)and depressions (wave troughs) of the thermoplastic film describe theproduction-related, actually undesirable surface waviness and are causedthereby. Typically, the distance between adjacent elevations or thedistance between adjacent depressions is greater than or equal to 50 mm.This must be distinguished from a desired surface roughness that isoften deliberately embossed into the film surface in the form ofelongated elevations and depressions to promote deaeration duringlamination of the composite pane, where the distance between adjacentelevations or depressions is typically less than 1 mm.

Essential to the present invention is the fact that the elongatedelevations (and elongated depressions) at least of one pane made of flatglass are arranged at an angle different from 90° relative to theextrusion direction of the thermoplastic film, i.e., at an angledifferent from 90° relative to the elongated elevations (and elongateddepressions) of the thermoplastic film. Advantageously, the elongatedelevations are arranged at an angle from 0° to 45°, particularlypreferably 0°, relative to the extrusion direction of the thermoplasticfilm.

As the inventors have perceived for the first time, flat glass panesadapt during lamination to the shape of the thermoplastic film and,thus, assume a certain waviness due to the waviness of the thermoplasticfilm. This effect occurs especially with very thin flat glass panes withthicknesses of less than 2.1 mm. As the inventors have found, anadvantageous effect on the local lens effect of the pane can be achievedthrough the claimed relative arrangement at least of one pane havingproduction-related waviness and the thermoplastic film. Without beingbound by any theory, it is stated that by means of the waviness imposedon the pane by the thermoplastic film, a compensation or equalization ofthe production-related waviness of the pane can be achieved such thatrelatively large differences in the local optical refractive power arereduced. The optical properties of the pane are thus significantlyimproved; in particular, there are smaller distortions of objects inthrough-vision. For this purpose, the elongated elevations at least ofone pane are advantageously arranged at an angle from 0° to 45° relativeto the extrusion direction of the thermoplastic film, with the currentassumption that the best effect in terms of a reduction of largedifferences in local optical refractive power can be achieved when theelongated elevations of a pane are arranged at an angle of 0° relativeto the extrusion direction of the thermoplastic film.

The intended effect occurs especially with very thin panes, wherein itis preferred according to the invention for at least one pane withproduction-related elongated elevations and depressions to have a panethickness of less than 2.1 mm. The inventors were able to demonstratethat with such thin panes, a particularly strong effect can be achievedin terms of a reduction in large differences in the local opticalrefractive power, since, on the one hand, the float lines or draw linesare stronger with thinner panes and, on the other, thin panes undergo astronger change due to the waviness of the thermoplastic film duringlamination. Particularly advantageously, at least one pane withproduction-related waviness has a pane thickness in the range from 0.5mm to 1.1 mm. Such thin panes are advantageously produced in the fusiondraw method. The inventors were able to demonstrate that for this panethickness, the effect according to the invention (improvement of opticalproperties) is particularly strong.

In one advantageous embodiment of the invention, one pane withproduction-related waviness has a pane thickness of less than 2.1 mm andthe other pane (which can also have production-related waviness) has apane thickness in the range from 1.4 mm to 2.6 mm. If both panes arerelatively thin, it can advantageously be achieved that the intendedeffect according to the invention occurs significantly with both panes.Alternatively, if one pane is thicker, it can advantageously be achievedthat the effect according to the invention occurs significantly only forthe thinner pane, while an improvement in the stability of the compositepane is achieved by means of the thicker pane.

In another advantageous embodiment of the invention, one pane withproduction-related waviness has a pane thickness of less than 2.1 mm andthe other pane (which can also have production-related waviness) has apane thickness of at least 2.1 mm, which is in particular within therange from 2.1 mm to 2.6 mm. Here, on the one hand, the advantageouseffect of the invention occurs significantly with the thinner pane; onthe other, a significant improvement in the stability of the compositepane results from the thicker pane.

According to the present invention, the first pane and/or the secondpane can be provided with elongated elevations and depressions (wavestructure) related to their production, with, for each pane, the abovestatements with reference to the relative arrangement of the elongatedelevations or depressions of the pane and the thermoplastic filmapplying separately. In particular, in the case of two relatively thinpanes (pane thickness less than 2.1 mm), a particularly good improvementof the optical properties of the composite pane can be achievedaccording to the invention.

The thermoplastic film contains at least one thermoplastic polymer,preferably ethylene vinyl acetate (EVA), polyvinyl butyral (PVB), orpolyurethane (PU) or mixtures or copolymers or derivatives thereof,particularly preferably PVB. The thickness of the thermoplastic film is,for example, 0.2 mm to 2 mm and is, in particular, within the range from0.3 mm to 1 mm.

The first and/or second pane with production-related waviness is a flatglass, in particular a float glass produced in the float glass method ora thin glass produced in the fusion draw method. It can, for example, bea quartz glass, borosilicate glass, aluminosilicate glass, or soda limeglass. Very thin glasses with thicknesses within the range from, forexample, 0.5 mm to 1.1 are, in particular, produced in the fusion drawmethod.

In the installed state, composite panes of the windshield type usuallyhave two pane edges extending in the vertical direction, which, forexample, are adjacent the nearest body struts, e.g., A pillars, as wellas two pane edges extending in the transverse direction, which arearranged, for example, on the roof side and on the engine compartmentside. The production-related elongated elevations and elongateddepressions of the at least one individual pane, in particular, bothindividual panes, typically run vertically. In the industrial seriesproduction of composite panes, the thermoplastic film necessary forlamination is typically rolled up along the extrusion direction andunrolled accordingly. According to one embodiment of the invention, thethermoplastic film is cut to length and laminated with the twoindividual panes such that the elongated elevations of the thermoplasticfilm are arranged parallel to the production-related elongatedelevations of the composite pane and, consequently, extend in thevertical direction.

The invention further relates to a method for producing a composite paneaccording to the invention as described above. It comprises thefollowing steps:

-   -   Providing the first pane,    -   Providing the second pane,        wobei at least one pane is in the form of a flat glass and has        elongated elevations and elongated depressions on at least one        surface,    -   Laminating the two panes with a thermoplastic film arranged        between the two panes, wherein the thermoplastic film has        elongated elevations and elongated depressions on at least one        surface,        wherein the two panes and the thermoplastic film are arranged        such that the elongated elevations of the at least one pane and        the elongated elevations of the thermoplastic film are oriented        at an angle different from 90°.

The invention further extends to the use of the composite pane accordingto the invention in means of transportation for travel on land, in theair, or on water, in particular in motor vehicles and in particular as awindshield in a motor vehicle.

The aforementioned embodiments and features of the invention can beprovided alone or in any combinations.

The invention is now explained in detail using exemplary embodimentswith reference to the accompanying figures. They depict:

FIG. 1 a schematic representation of a thermoplastic film partiallyunwound from a roll;

FIG. 2 a cross-sectional view of the thermoplastic film along thesection line A-A of FIG. 1;

FIG. 3 a schematic representation of the arrangement of individual panesfor the cutting of the thermoplastic film of FIG. 1;

FIG. 4 an exploded representation of the composite pane according to apreferred embodiment of the invention;

FIG. 5 a composite pane, in particular a windshield of a motor vehicle,according to a preferred embodiment of the invention;

FIG. 6 a diagram illustrating the local optical refractive power of aprior art composite pane (left) and a composite pane according to theinvention (right);

FIG. 7 a flowchart of a method for producing the composite paneaccording to the invention in accordance with a preferred embodiment ofthe invention.

FIG. 1 is a schematic representation of a thermoplastic film 4 partiallyunwound from a roll 5. The thermoplastic film 4 is preferably made ofPVB. Alternatively, the thermoplastic film can be made of anothersuitable material, such as polyamide or polyethylene. The thermoplasticfilm 4 is produced by extrusion, with the extrusion direction of thethermoplastic film 4 corresponding to the winding or unwinding directionof the roll 5. In FIG. 1, the direction of extrusion or unwinding isindicated by the arrow R1.

FIG. 2 depicts a cross-sectional view of the thermoplastic film 4 alongthe section line A-A drawn in FIG. 1. At least one surface 6 of thethermoplastic film 4 is discernibly wavy and has, in parallelarrangement, a plurality of elongated elevations 7 projecting from thesurface 6 (hereinafter referred to as film elevations 7) and elongateddepressions 8 deepening the surface 6 (hereinafter referred to as filmdepressions 8). The film elevations 7 and film depressions 8 extend ineach case in the extrusion direction R1. Transverse to the extrusiondirection, the film elevations 7 and film depressions 8 arealternatingly arranged. The film elevations 7 and film depressions 8 arewave-shaped such that the surface 6 of the thermoplastic film has awaviness. It should be noted that FIG. 2 is only a schematicrepresentation; typically, the opposite surface 6′ is correspondinglywavy and provided with film elevations 7 and film depressions 8.

FIG. 3 is a schematic representation to illustrate a preferredembodiment of (individual) panes 2, 3 relative to the thermoplastic film4 for producing a composite pane according to the invention 1.Accordingly, the thermoplastic film 4 is cut to length such that thepane edges extending, in the installed state, in the transversedirection of the vehicle are arranged transversely to the extrusiondirection R1.

FIG. 4 is an exploded representation of the composite pane 1 inaccordance with a preferred embodiment of the invention. The compositepane 1 comprises a first pane 2 and a second pane 3, as well as, betweenthe two panes 2, 3, a thermoplastic film 4, which is cut to length fromthe roll 5. Each pane 2, 3 has, related to its production, a pluralityof elongated elevations 11 projecting from the surface 13 (hereinafterreferred to as pane elevation 11) and elongated depressions 12 deepeningthe surface 13 (hereinafter referred to as pane depression 12) inparallel arrangement. The pane elevations 11 and pane depressions 12extend in each case along a direction that is indicated in FIG. 4 by thearrow R2. The pane elevations 11 and pane depressions 12 arealternatingly arranged transverse to the direction R2. The paneelevations 11 and pane depressions 12 are wave-shaped such that thesurface 13 of each of the two panes 2, 3 has a waviness. Typically, bothopposite surfaces 13, 13′ of each pane 2, 3 are wave-shaped and havepane elevations 11 and pane depressions 12.

As illustrated in FIG. 4, in the laminated state, the pane elevations 11and pane depressions 12 of the first pane 2 are arranged parallel to thepane elevations 11 and pane depressions 12 of the second pane 3. Inaddition, the pane elevations 11 and pane depressions 12 of the twopanes 2, 3 are arranged parallel to the extrusion direction R1 orparallel to the film elevations 7 and film depressions 8.

Furthermore, the first pane 2 is thinner than 2.1 mm. The pane thicknessof the second pane 3 is within the range from 0.5 mm to 1.1 mm.Alternatively, provision can be made for the pane thickness of thesecond pane 3 to be greater than 2.1 mm and in particular within therange from 2.1 mm to 2.6 mm. The first pane 2 and second pane 3 are madeof glass and are, for example, produced in the float glass method or afusion draw method. It is also conceivable for only the first pane 2 tobe made of glass and have pane elevations 11 and pane depressions 12,and for the second pane 3 to be made of a polymer.

FIG. 5 depicts another embodiment of the composite pane according to theinvention 1, in particular for use as a windshield of a motor vehicle.As illustrated in FIG. 5, the composite pane 1 comprises a first pane 2,a second pane 3, and a thermoplastic film 4. The composite pane 1 hasfour pane edges, namely an upper pane edge 9 and a lower pane edge 10,which extend, in the installed state, in the (vehicle's) transversedirection, and two side pane edges 14, which extend, in the installedstate, in the (vehicle's) vertical direction. The film elevations 7 andfilm depressions 8 extend in each case along a shortest connection linebetween the upper pane edge 9 and the lower pane edge 10 (i.e.,extrusion direction R1). The first and/or second pane 2, 3 is flat glassand has pane elevations 11 and pane depressions 12, which also extendalong a shortest connection line between the upper pane edge 9 and thelower pane edge 10 (i.e., pulling direction R2).

FIG. 6 depicts a diagram in which the optical refractive power D of aprior art composite pane (left) and a composite pane according to theinvention 1 (right) is indicated. The first pane 2 is a 0.5-mm-thickaluminosilicate glass that is produced in the fusion draw method; thesecond pane 3 is a 2.1-mm-thick soda lime glass that is produced in thefloat glass method.

In the two images on the left, which correspond to the prior art case,the extrusion direction R1 of the thermoplastic film 4 is oriented at anangle of 90° relative to the direction R2 of the pane elevations 11 andpane depressions 12 of the two panes 2, 3. In the two images on theright, which correspond to the invention, the extrusion direction R1 ofthe thermoplastic film 4 is oriented at an angle of 0° relative to thedirection R2 of the pane elevations 11 and pane depressions 12 of thetwo panes 2, 3, in other words, the extrusion direction R1 and thedirection R2 are parallel to each other.

In the diagram, the optical refractive power D [mdpt] in through-visionthrough the composite panes is illustrated using different shades ofgray. The two upper images report the horizontal optics (i.e., thechange in the optical refractive power in the horizontal direction)(Case A). The two lower images report the vertical optics (i.e., thechange in the optical refractive power in the vertical direction) (CaseB).

As is readily discernible from the two upper images (Case A), asignificant reduction in the changes of the optical refractive power Dcan be achieved, especially in the interior region, with the compositepane according to the invention (right image). Compared to the prior artcase, the optical refractive power D of the composite pane issubstantially more homogeneous such that the through-vision is improved.With regard to the vertical optics (Case B, lower images), a slightworsening appears to occur with the invention (amplification of thechanges in the optical refractive power D); however, this is hardlynoticeable in practice since the changes in the optical refractive powerD in the vertical direction are typically far less distracting thanchanges in the optical refractive power in the horizontal direction.Thus, by means of the composite pane according to the invention, asignificant improvement of the optical properties in through-vision isachieved.

FIG. 7 depicts a flowchart of a method for producing the composite paneaccording to a preferred embodiment of the invention.

The method comprises providing (S1) the first pane 2, providing (S2) thesecond pane 3, and laminating (S3) the two panes 2, 3 with athermoplastic film 4 arranged between the two panes, wherein the twopanes 2, 3 and the thermoplastic film 4 are arranged such that theproduction-related pane elevations 11 and pane depressions 12 of thefirst pane 2 and/or the second pane 3 are oriented at an angle differentfrom 90°, in particular at an angle from 0° to 45°, preferably 0°,relative to the extrusion direction of the thermoplastic film 4.

From the statements above, it can be seen that the invention provides acomposite pane with significantly reduced local changes in the opticalrefractive power and, consequently, improved through-vision. Prior artmethods for producing composite panes can easily be modified to achieveeconomical production of the composite

LIST OF REFERENCE CHARACTERS

-   1 composite pane-   2 first pane-   3 second pane-   4 thermoplastic film-   5 roll-   6, 6′ film surface-   7 film elevation-   8 film depression-   9 upper pane edge-   10 lower pane edge-   11 pane elevation-   12 pane depression-   13, 13′ pane surface-   14 side edge of the pane

1. Composite pane that comprises a first pane, a second pane, and atleast one thermoplastic film arranged between the first and secondpanes, wherein at least one pane of the first and second panes is in theform of a flat glass and at least one pane surface has a plurality ofelongated elevations and elongated depressions that extend along a firstpane direction and are alternatingly arranged in a second pane directionperpendicular to the first pane direction, the thermoplastic film isproduced by extrusion and at least one film surface has a plurality ofelongated elevations and elongated depressions that extend along a firstfilm direction and are alternatingly arranged in a second film directionperpendicular to the first film direction, wherein the elongatedelevations of the at least one pane are arranged at an angle differentfrom 90° relative to the elongated elevations of the thermoplastic film.2. The composite pane according to claim 1, wherein a distance betweenadjacent elevations and a distance between adjacent depressions of thethermoplastic film are greater than or equal to 50 mm.
 3. The compositepane according to claim 1, wherein the elongated elevations of the atleast one pane are arranged at an angle from 0° to 45° relative to theelongated elevations of the thermoplastic film.
 4. The composite paneaccording to claim 1, wherein the at least one pane with elongatedelevations and elongated depressions has a pane thickness of less than2.1 mm hat.
 5. The composite pane according to claim 4, wherein the atleast one pane with elongated elevations and elongated depressions has apane thickness in the range from 0.5 mm to 1.1 mm.
 6. The composite paneaccording to claim 4, wherein the at least one pane has elongatedelevations and elongated depressions and has a pane thickness of lessthan 2.1 mm, and the other pane has a pane thickness in the range from1.4 mm to 2.6 mm.
 7. The composite pane according to claim 4, whereinthe at least one pane has elongated elevations and elongated depressionsand has a pane thickness of less than 2.1 mm, and the other pane has apane thickness of at least 2.1 mm.
 8. The composite pane according toclaim 1, wherein the first pane and second pane each have elongatedelevations and elongated depressions.
 9. The composite pane according toclaim 8, wherein the elongated elevations and elongated depressions ofthe first pane are arranged parallel relative to the elongatedelevations and elongated depressions of the second pane.
 10. Thecomposite pane according to claim 1, wherein the at least one pane withelongated elevations and elongated depressions is produced in the floatglass method or the fusion draw method.
 11. The composite pane accordingto claim 1, wherein the thermoplastic film is made of polyvinyl butyral(PVB).
 12. The composite pane according to claim 1, comprising two paneedges extending in a transverse direction in an installed state and twopane edges extending in a vertical direction in the installed state,wherein the elongated elevations and elongated depressions of the firstpane and/or the second pane extend along a line.
 13. Method forproducing a composite pane according to claim 1, the method comprising:providing the first pane, providing the second pane, laminating thefirst and second panes with at least one thermoplastic film arrangedbetween the first and second panes, wherein the first and second panesand the thermoplastic film are arranged such that the elongatedelevations at least of one pane of the first and second panes arearranged at an angle different from 90° relative to the elongatedelevations of the thermoplastic film.
 14. A method comprising utilizinga composite pane according to claim 1 in means of transportation fortravel on land, in the air, or on water.
 15. The composite paneaccording to claim 3, wherein the elongated elevations of the at leastone pane are arranged at an angle of 0° relative to the elongatedelevations of the thermoplastic film.
 16. The composite pane accordingto claim 7, wherein the other pane has a pane thickness in the rangefrom 2.1 mm to 2.6 mm.
 17. The composite pane according to claim 12,wherein the line is the shortest line that connects the two pane edgesextending in the transverse direction to one another.
 18. The methodaccording to claim 14, wherein the composite pane is a windshield in amotor vehicle.